Sanding devices are widely used in a wide variety of manufacturing operations. For example, in the automobile manufacturing industry, sanding systems are used to prepare the metal surface of the car body for receiving one or more coats of paint primer, and one or more finishing coats of paint. Frequently, one or more of the intermediate layers of paint must be sanded or touched up by sanding in order to smooth rough edges and other imperfections in the finish before the final coat of paint is applied.
Sanding is a necessary procedure in providing a smooth surface to the finished article and is therefore virtually indispensable. However, there has been a perennial problem associated with any sanding operation, and even more so with sanding operations that are conducted using high speed mechanical equipment. The material that is sanded away from the surface being prepared is given off in the form of a fine dust. Frequently, this dust is so light that it hangs in the air for a period of time before settling.
In large scale sanding operations, using high speed mechanical equipment, a large quantity of fine dust is generated which creates very uncomfortable working conditions for the workmen. The fine dust floats in the air for a considerable amount of time and is breathed in by the workmen, settles on their clothing, and all exposed surfaces surrounding the sanding operation. The dust is therefore an acute nuisance.
Many attempts in the past have been made to reduce the dusting problem associated with high speed, large scale sanding operations. One method of reducing the dusting problem, particularly in automobile manufacturing plants, is to continuously bathe the working surface with a moving film of water that carries away the fine material that has been abraded away by the sanding machine. This is known as "wet sanding". However, this system, while it keeps dusting to a minimum, uses considerable quantities of water, and makes working conditions uncomfortable for the workmen. The workmen must wear waterproof clothing, and the generally wet conditions throughout the sanding plant create a cold and uncomfortable environment.
It would be preferably if a "dry sanding" system, which did not have a dusting problem, could be devised. Efforts in this direction have been made by attempting to suck the dust out of the air by means of a vacuum system. However, these efforts to date have been only marginally successful. It has been possible to draw away only a small proportion of the dust by using the systems designed to date. Considerable dust remains in the air and is inhaled by the workmen and settles on the workpiece as well as surrounding objects.
A further problem associated with "dry sanding" metal and plastic objects is that the abraded materials develops an electrostatic charge which causes the dust to adhere to the surface of the workpiece being sanded. Vacuum systems designed to date have been unsuccessful in removing the dust that clings electrostatically to the surface of the workpiece.
To alleviate the foregoing problems associated with "dry sanding", I have previously developed a vacuum sanding system that is very effective in drawing away the dust developed by the sanding machine. My system is disclosed and claimed in copending Canadian patent application Ser. No. 148,535, filed Aug. 2, 1972. The system disclosed uses a vacuum chamber that encloses the sanding pad and sanding disc. The chamber has a plurality of openings that are distributed about the periphery of the circular sanding disc of the sanding device. This system has the advantage of placing the vacuum opening very close to the area of the workpiece where the material is being abraded free of the workpiece, and, as a consequence, almost no dust escapes being drawn away by one of the vacuum openings.
However, while very efficient, this vacuum system has two disadvantages. The vacuum housing obscures the sanding disc and backup pad from view by the workman. As a result, the workman doing the sanding is not able to see the edge of the sanding disc as it sands away the material from the workpiece. A considerable amount of sanding is done on special areas, using only one side of the sanding disc, and in order to sand these areas smoothly, the workman prefers to be able to see the surface as it is being sanded. This not possible with the vacuum chamber system since it encloses and hides the sanding disc.
The second disadvantage is that the vacuum chamber surrounding the sanding disc acts as a bumper of sorts and prevents the sanding disc from running up to the extreme edge of any workpiece that has an upraised border to obstruction on it. In such situations, it is necessary to sand the unsanded border areas using a sanding device that does not have a vacuum chamber surrounding the sanding dics. This is a nuisance, is time consuming and generates a certain amount of dust that coats the other area of the workpiece.